"However, when this road is built it will not interfere with the natural environment."

That comment was met with loud boos.

The rally was held in tandem with a protest at the Roe 8 site at Bibra Lake, where dozens of police arrived after protesters sat down to block a drilling crew.

While Labor said that was a waste of police resources, the activists were incensed to see work underway when a hearing for a Supreme Court challenge to the Roe 8 environmental approval is scheduled for next week.

Mr Barnett said the crew was checking conditions in the water table.

"That is all it is," he said.

"They weren't under construction."

Mr Barnett said the construction contracts would be awarded before Christmas.

Transport Minister Dean Nalder was also jeered when he spoke to the crowd.